Stator and rotor stacks in electric motors and generators as well as lamination stacks of transformers are produced from so-called electrical strip. Electrical strip is a strip steel sheet, for example with thicknesses of between 0.1 mm and 2 mm.
This strip steel sheet is stamped into the required shapes and the individually stamped components are assembled into corresponding stacks, which are then processed to produce finished electric motors, generators, or transformers. In these stamping processes, in order to reduce waste, usually both the rotor parts and the stator parts are stamped out of the same sheet and therefore have correspondingly similar properties. If an iron core (stacked sheets) of this kind is used in a coil, then its ferromagnetic properties—which are preset or at the least prepared by the steel manufacturer so that they are set by the user through a finish annealing—increase the permeability and therefore also the magnetic flux density in the coil. As a result, it is possible to reduce the number of windings needed to achieve a required inductance.
Because the iron of the core is an electrical conductor, in a coil with an iron core through which alternating current is flowing, a current flows in a quasi-short-circuit is winding, which is referred to as eddy current. This eddy current is reduced if the core is not made out of a single piece of iron, but rather out of a stack of the above-described iron sheets.
Electrical strips of this kind are composed of a relatively soft steel material. Particularly in the production of motors and generators, it is of interest for the manufacturer to reduce the air gaps because this increases the magnetic effectiveness; on the other hand, particularly with very high speed motors and in particular generators, very powerful centrifugal forces occur. Particularly in generators, the rotors can be relatively large so that the moving masses can produce very powerful centrifugal forces. These very powerful centrifugal forces on the one hand result in the fact that a stretching occurs so that very narrow air gaps are difficult to implement and on the other hand, the powerful centrifugal forces can also result in a failure of the rotor material.
In order to counteract these problems, it is known from the prior art to provide electrical strip with higher strength properties.
In order to increase the strength properties of electrical strip, it is customary to work with aluminum/silicon alloy concepts. Such alloy concepts are known, for example, from JP 2010090474 A, in which a relatively high silicon content is used. A general overview is provided by a paper from the “4th International Conference on Magnetism and Metallurgy,” WMM '10, Freiburg, Germany, “Magnetic and Mechanical Properties of Newly Developed High-Strength Non-Oriented Electrical Steel,” pages 277 through 281.
In addition, EP 2031 079 A1 has disclosed a high-strength electromagnetic steel strip and a method for the production thereof. This document has disclosed that copper increases the degree of recrystallization; the content should be less than 0.1 mass %, in particular less than 0.01 mass %.
The object of the invention is to create a method for producing a higher-strength non-grain-oriented electrical strip, which strip, in addition to a high strength, has good magnetic properties.